The seven different serotypes of botulinum neurotoxins (BoNTs) are among the most toxic substances in the world. They prevent neurotransmitter release by proteolytically cleaving proteins required for vesicle fusion. No antidote is available except for equine antisera. We propose to use high throughput screening of chemical libraries to identify inhibitors of two steps in toxin action: (i) membrane channel formation of botulinum neurotoxin (BoNT) heavy chains, required for toxin internalization, and (ii) endopeptidase activities of BoNT light chains against their known protein substrates.